1. Field of the Invention
The present invention relates to a machine tool that machines a workpiece using tools.
2. Background Art
As the number of machined workpieces is increasing, a cutting edge of a tool is worn out. That is, the position of the cutting edge of the tool is displaced due to wear. For this reason, the position of the cutting edge of the tool (the machining point of the tool relative to the workpiece) needs to be corrected according to the amount of wear. Further, a tool, which is significantly worn out, needs to be replaced with a new tool.
In this respect, JP-A-2004-30421 discloses an NC machine tool that can display the change of a correction amount of the position of a cutting edge as a graph. According to the NC machine tool disclosed in JP-A-2004-30421, a worker can visually recognize the change of a correction amount of the portion of the cutting edge relative to the number of workpieces that are machined after the replacement of a tool or time that has elapsed from the start of operation. For this reason, a worker can determine a correction amount to be input while viewing graphs (viewing the past correction history).
Incidentally, the position of the cutting edge of the tool is displaced due to heat in addition to the wear of the above-mentioned cutting edge. Specifically, a workpiece is mounted on a headstock by a chuck. Meanwhile, the tool is mounted on a tool rest. The headstock and the tool rest generate heat with the operation of the machine tool. For this reason, a relative positional relationship between the workpiece and the cutting edge of the tool is changed. That is, the position of the cutting edge of the tool is displaced.
Further, the ambient temperature in a factory is changed due to the outdoor temperature, the number of people in the factory, the driving heat of machines disposed in the factory, and the like. The relative positional relationship between the workpiece and the cutting edge of the tool is changed even due to the change of the ambient temperature. For this reason, it is necessary to consider the influence of heat when correcting the position of the cutting edge of the tool.
However, in the case of the NC machine tool disclosed in JP-A-2004-30421, it has been difficult to grasp the influence of heat on the position of the cutting edge of the tool from the graph to be displayed. For this reason, it has been difficult for a worker to input a correction amount in consideration of the influence of heat.